MANILA — The Philippines‘ president announced Sunday that his government has reached a preliminary peace deal with the nation’s largest Muslim rebel group in a major breakthrough toward ending a decades-long insurgency.

President Benigno Aquino III said the “framework agreement” — a road map for a new autonomous region for minority Muslims in the predominantly Roman Catholic nation’s south — was an assurance the Moro Islamic Liberation Front insurgents will no longer aim to secede from the country.

The agreement, which is to be signed Oct. 15 in Manila, spells out general principles on major issues, including the extent of power, revenues and territory of the Muslim region.

If all goes well, a final peace deal could be reached by 2016, when Mr. Aquino’s six-year term ends, officials said.

“This framework agreement paves the way for final and enduring peace in Mindanao,” Mr. Aquino said, referring to the southern Philippine region and homeland of the country’s Muslims. “This means that the hands that once held rifles will be put to use tilling land, selling produce, manning work stations and opening doorways of opportunity.”

He cautioned, however, that “the work does not end here,” and that the two sides still need to work out the accord’s details.

Those talks are expected to be tough but doable, officials and rebels said.

Rebel Vice Chairman Ghadzali Jaafar said the agreement provides a huge relief to people who have long suffered from war and are “now hoping the day would come when there will be no need to bear arms.”

The deal marks the most significant progress in 15 years of on-and-off negotiations with the 11,000-strong Moro group on ending an uprising that has left more than 120,000 people dead, displaced about 2 million others and held back development in the south. Western governments have long worried that rebel strongholds could become breeding grounds for al Qaeda-affiliated extremists.

“The parties agree that the status quo is unacceptable,” the 13-page agreement says. It calls for the creation of a new Muslim autonomous region called “Bangsamoro” to replace an existing one created in 1989 that Mr. Aquino characterized as a “failed experiment,” where poverty and corruption have forced many “to articulate their grievances through the barrel of a gun.”

The accord also calls for the establishment of a 15-member “Transition Commission” to work out the details of the preliminary agreement and draft a law creating the new Muslim autonomous region in about two years.

Rebel forces would be deactivated gradually “beyond use,” the agreement says, without specifying a timetable.

The Philippine government would continue to exercise exclusive powers over defense and security, foreign and monetary policy in the new autonomous region, where Muslims would be assured of an “equitable share of taxation, revenues, and the fruits of national patrimony and equal protection of laws and access to impartial justice,” according to Mr. Aquino.

Philippine officials said the preliminary accord would be posted on the government’s website for public scrutiny, and would be signed in Manila in the presence of Mr. Aquino, Malaysian Prime Minister Najib Razak and Moro rebel chief Al Haj Murad Ibrahim.

“It’s been a long journey and this is an important milestone in our search for lasting peace,” presidential peace talks adviser Teresita Deles told AP.

The U.S., Britain, Malaysia and other countries welcomed the accord.

“This agreement is a testament to the commitment of all sides for a peaceful resolution to the conflict in the southern Philippines,” Secretary of State Hillary Rodham Clinton said in a statement. “The next steps will be to ensure that the framework agreement is fully implemented.”

The new Muslim region would be built upon an existing five-province autonomous territory, among the country’s poorest and most violent, with more than 4 million people.

The Moro rebels earlier dropped a demand for a separate Muslim state and renounced terrorism.